The mica variety that does not contain iron is colorless in flakes, and the higher the iron content, the darker the color, and the more polychromatic and absorbable it is. According to the different chemical composition and optical characteristics, mica group minerals can be divided into Muscovite subgroup, biotite-phlogopite subgroup and lemica subgroup. The common mica are biotite, phlogopite, Muscovite and so on.

The mica variety that does not contain iron is colorless in flakes, and the higher the iron content, the darker the color, and the more polychromatic and absorbable it is. According to the different chemical composition and optical characteristics, mica group minerals can be divided into Muscovite subgroup, biotite-phlogopite subgroup and lemica subgroup. The common mica are biotite, phlogopite, Muscovite and so on.

The common characteristics of mica group minerals are: layered silicate minerals, monoclinic crystal system, a few trigonal crystal system, the crystals are pseudo-hexagonal columnar, plate and sheet; The aggregate is scaly and foliaceous. It has a set of extremely complete cleavage, along which it is easy to peel into sheets. Therefore, the shape of mica is usually regarded as sheet.

X represents large interlayer cations, such as K+, Na+, Ca2+, Ba2+, Rb+, Cs+, etc. Y represents octahedral cations, such as Al3+, Fe2+, Mg2+, Cr3+, Ti4+, Fe3+, etc. Z is mainly Si4+ and Al3+; The ideal ratio of the additional anion (OH)- to (O)2- is 2:10, and (OH)- can be replaced by F- and Cl-. Most mica contain 4% to 5% water. Therefore, although they may be called mica, the chemical composition of different mica may be very different, for the purpose of research, we collectively refer to the minerals with this type of characteristics as mica group minerals.